//https://leetcode.cn/problems/merge-two-sorted-lists/
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        if(list1==nullptr)return list2;
        if(list2==nullptr)return list1;
        if(list1->val < list2->val){
           list1->next=mergeTwoLists(list1->next,list2);
           return list1;
        } else{
            list2->next= mergeTwoLists(list1,list2->next);
              return list2;
        }
    }
};
